U.S. patent application number 11/659338 was filed with the patent office on 2008-05-29 for hard multilayer coating, and hard multiyayer coated tool including the hard multilayer coating.
This patent application is currently assigned to Osg Corporation. Invention is credited to Hiroyuki Hanyu, Takaomi Toihara.
Application Number | 20080124531 11/659338 |
Document ID | / |
Family ID | 37835428 |
Filed Date | 2008-05-29 |
United States Patent
Application |
20080124531 |
Kind Code |
A1 |
Hanyu; Hiroyuki ; et
al. |
May 29, 2008 |
Hard Multilayer Coating, and Hard Multiyayer Coated Tool Including
the Hard Multilayer Coating
Abstract
A hard multilayer coating including: (a) a backing layer which
is to be disposed on a body and which includes a TiAIN layer and a
TiAlN+CrN mixture layer that are alternately superposed on each
other; and (b) a CrN layer which is disposed on the backing layer
and which provides an outer surface of the hard multilayer coating.
The hard multilayer coating may further includes (c) an
intermediate layer which is interposed between the backing layer
and the CrN layer. Also disclosed is a hard multilayer coated tool
including a tool substrate as the body which is coated with the
hard multilayer coating.
Inventors: |
Hanyu; Hiroyuki; (Aichi-ken,
JP) ; Toihara; Takaomi; (Aichi-ken, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
Osg Corporation
Aichi-ken
JP
|
Family ID: |
37835428 |
Appl. No.: |
11/659338 |
Filed: |
September 1, 2005 |
PCT Filed: |
September 1, 2005 |
PCT NO: |
PCT/JP05/16043 |
371 Date: |
February 28, 2007 |
Current U.S.
Class: |
428/216 ;
428/697 |
Current CPC
Class: |
C23C 28/044 20130101;
Y10T 428/24975 20150115; B23C 2228/10 20130101; C23C 30/005
20130101; B23C 2224/13 20130101; C23C 30/00 20130101; C23C 28/42
20130101; C23C 14/024 20130101; B23C 5/1009 20130101; Y10T 428/265
20150115; B23C 2224/24 20130101; C23C 14/0641 20130101 |
Class at
Publication: |
428/216 ;
428/697 |
International
Class: |
B32B 7/02 20060101
B32B007/02; B32B 9/04 20060101 B32B009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2004 |
JP |
2004-3500165 |
Claims
1-7. (canceled)
8. A hard multilayer coating comprising: a backing layer that is to
be disposed on a body, said backing layer including a TiAlN layer
and a TiAlN+CrN mixture layer that are alternately superposed on
each other; an intermediate layer disposed on said backing layer
and consisting of a TiAlN+CrN mixture layer; and a CrN layer
disposed on said intermediate layer and providing an outer surface
of said hard multilayer coating.
9. The hard multilayer coating according to claim 8, wherein said
backing layer has a thickness of from 2 .mu.m to 8 .mu.m; wherein
said intermediate layer has a thickness of from 0.1 .mu.m to 5
.mu.m; wherein said CrN layer has a thickness of from 0.1 .mu.m to
5 .mu.m; and and wherein said hard multilayer coating has an entire
thickness of not larger than 10 .mu.m.
10. A hard multilayer coating comprising: a backing layer that is
to be disposed on a body, said backing layer including a TiAIN
layer and a TiAIN+CrN mixture layer that are alternately superposed
on each other; and a CrN layer disposed on said backing layer and
providing an outer surface of said hard multilayer coating.
11. The hard multilayer coating according to claim 10, wherein said
backing layer has a thickness of from 2 .mu.m to 8 .mu.m; wherein
said CrN layer has a thickness of from 0.1 .mu.m to 8 .mu.m; and
and wherein said hard multilayer coating has an entire thickness of
not larger than 10 .mu.m.
12. The hard multilayer coating according to claim 8, wherein a
lowermost layer and an uppermost layer of said backing layer is
provided by said TiAIN layer.
13. The hard multilayer coating according to claim 10, wherein a
lowermost layer and an uppermost layer of said backing layer is
provided by said TiAIN layer.
14. The hard multilayer coating according to claim 8, wherein said
hard multilayer coating is to be disposed on a surface of a cutting
tool.
15. The hard multilayer coating according to claim 10, wherein said
hard multilayer coating is to be disposed on a surface of a cutting
tool.
16. A hard multilayer coated tool comprising: the hard multilayer
coating defined in claim 8; and a tool substrate that is coated
with said hard multilayer coating.
17. A hard multilayer coated tool comprising: the hard multilayer
coating defined in claim 10; and a tool substrate that is coated
with said hard multilayer coating.
Description
TECHNICAL FIELD
[0001] The present invention relates in general to a hard
multilayer coating, and more particularly to such a hard multilayer
coating that has high lubricity (welding resistance) in addition to
excellent wear resistance and tenacity.
BACKGROUND ART
[0002] There is proposed a hard multilayer coated tool that is
constituted by (i) a tool substrate made of high-speed tool steel
or cemented carbide and (ii) a hard multilayer coating disposed on
a surface of the tool substrate. The hard multiplayer coating
includes a TiAlN layer and a mixture layer of TiAlN+CrN that are
alternately superposed on each other. As an example of the hard
multilayer coated tool, Patent Document 1 discloses a rotary
cutting tool including a TiAlN layer and a mixture layer that are
alternately superposed on each other, wherein the TiAlN layer has a
high hardness while the mixture layer includes CrN whose hardness
is relatively low. In the disclosed rotary cutting tool, an
excellent wear resistance is obtained owing to presence of the
TiAlN layer having the high hardness, while an increased tenacity
is obtained owing to presence of the mixture layer including CrN
whose hardness is relatively low, so that chipping and peeling of
the coating is restrained whereby durability of the tool is
substantially increased.
Patent Document 1: JP-2002-275618A
DISCLOSURE OF INVENTION
Object to be Solved by the Invention
[0003] However, due to a relatively high coefficient of friction of
the above-described TiAlN layer, where the cutting tool is used for
cutting a workpiece that is made of an easily weldable material
such as copper and copper alloy, welding between the cutting tool
and the workpiece could be easily caused due to the high
coefficient of friction of the TiAlN layer. The welding
deteriorates the cutting performance such as machining accuracy,
and causes wear on the cutting tool in an early stage, thereby
making it impossible to obtain desired durability of the cutting
tool. For example, in a cutting operation with the rotary cutting
tool such as ball endmill and drill, the welding is easily caused,
particularly, in a portion of the rotary cutting tool that tends to
come into friction contact with the workpiece, such as a portion
around the axis of rotation and a portion constituting each rake
face.
[0004] The present invention was made in the light of the
background art discussed above. It is therefore an object of the
invention to improve a resistance against welding in a hard
multilayer coating that is constituted principally by TiAlN.
Measures for Achieving the Object
[0005] For achieving the above object, the first invention provides
a hard multilayer coating characterized by consisting of (a) a
backing layer disposed on a predetermined body and including a
TiAlN layer and a mixture layer of TiAlN+CrN that are alternately
superposed on each other; (b) an intermediate layer disposed on the
backing layer and consisting of a mixture layer of TiAlN+CrN; and
(c) a CrN layer disposed on the intermediate layer and providing a
surface of the hard multilayer coating.
[0006] The second invention is, in the hard multilayer coating of
the first invention, characterized in that: the backing layer has a
thickness of from 2 .mu.m to 8 .mu.m; the intermediate layer has a
thickness of from 0.1 .mu.m to 5 .mu.m; the CrN layer has a
thickness of from 0.1 .mu.m to 5 .mu.m; and an entire thickness of
the hard multilayer coating is not larger than 10 .mu.m.
[0007] The third invention provides a hard multilayer coating
characterized by consisting of (a) a backing layer disposed on a
predetermined body and including a TiAlN layer and a mixture layer
of TiAlN+CrN that are alternately superposed on each other; and (b)
a CrN layer disposed on the backing layer and providing a surface
of the hard multilayer coating.
[0008] The fourth invention is, in the hard multilayer coating of
the third invention, characterized in that: the backing layer has a
thickness of from 2 .mu.m to 8 .mu.m; the CrN layer has a thickness
of from 0.1 .mu.m to 8 .mu.m; and an entire thickness of the hard
multilayer coating is not larger than 10 .mu.m.
[0009] The fifth invention is, in the hard multilayer coating of
any one of the first through fourth inventions, characterized in
that each of a lowermost layer and an uppermost layer of the
backing layer is provided by the TiAlN layer.
[0010] The sixth invention is, in the hard multilayer coating of
any one of the first through fifth inventions, characterized in
that the hard multilayer coating is to be disposed on a surface of
a cutting tool.
[0011] The seventh invention provides a hard multilayer coated tool
characterized in that the hard multilayer coated tool is covered at
a surface thereof with the hard multilayer coating of any one of
the first through fifth inventions.
EFFECTS OF THE INVENTION
[0012] In the hard multilayer coating of each of the first through
sixth inventions, owing to presence of the backing layer including
the TiAlN layer and the mixture layer of TiAlN+CrN that are
alternately superposed on each other, it is possible to obtain
excellent wear resistance and tenacity. Further, since the CrN
layer constitutes an uppermost portion of the hard multilayer
coating and providing the surface of the hard multilayer coating
has a low coefficient of friction, it is possible to improve
lubricity and welding resistance. Further, since an oxidation
initiation temperature of the CrN layer is as high as about
700.degree. C., excellent characteristics of the coating are stably
maintained even in an environment of high temperature.
[0013] Therefore, where such a hard multilayer coating is applied
to a rotary cutting tool such as a ball endmill, it is possible to
obtain excellent cutting performance and durability in a wide range
of use, for example, from a case of cutting a workpiece made of
ferrous or non-ferrous (e.g., copper alloy) material having a low
hardness and easily weldable, to a case of cutting a workpiece made
of a high hardness material such as heat treated steel having a
hardness of about 50 HRC. Specifically described, owing to presence
of the CrN layer, it is possible to restrain wear on each rake face
and to restrain change of the rake angle toward the negative side
in a late stage of the cutting operation, so that a cutting
capacity is satisfactorily maintained for a long term, thereby
improving the durability of the tool and stabilizing the quality of
the finished surface of the workpiece. The rotary cutting tool such
as a ball endmill has a distal end portion which is located around
its axis of rotation, and the workpiece is easily weldable to the
distal end portion due to a low cutting capacity of the distal end
portion. However, owing to the presence of the CrN layer, the
welding can be restrained whereby the cutting performance and the
durability can be satisfactorily maintained. Further, since the
excellent characteristics of the coating can be stably obtained
even in the environment of high temperature, the cutting tool is
capable of carrying out a cutting operation with high efficiency
under a tough cutting condition with a high temperature caused by,
for example, frictional heat.
[0014] Further, in the first invention, since the intermediate
layer consisting of the mixture layer of TiAlN+CrN (including CrN)
is interposed between the backing layer and the CrN layer, the CrN
layer is superposed on the intermediate layer with high
adhesiveness, so that chipping and peeling of the CrN layer can be
further advantageously restrained.
[0015] In the fifth invention in which each of the lowermost layer
and the uppermost layer of the backing layer is provided by the
TiAlN layer, the backing layer can be adhered to the predetermined
body (e.g., tool substrate) with excellent adhesiveness owing to
the TiAlN layer providing the lowermost layer, while the backing
layer can have excellent wear resistance owing to the TiAlN layer
providing the uppermost layer. Since the CrN layer is disposed on
the TiAlN layer as the uppermost layer directly or through the
intermediate layer, the TiAlN layer having the high hardness is not
brought into direct contact with the workpiece. However, the TiAlN
layer serves to restrain deformation of the CrN layer, so that wear
resistance of the CrN layer is improved.
[0016] In the hard multilayer coated tool of the seventh invention,
it is possible to obtain substantially the same effect as in the
first through fifth inventions.
BRIEF DESCRIPTION OF DRAWINGS
[0017] [FIG. 1] A set of views showing an endmill that is one
embodiment of the present invention, wherein view (a) is a front
view as seen in a direction perpendicular to an axis of the
endmill, view (b) is an enlarged bottom view, and view (c) is a
cross sectional view of a layered portion of a cutting teeth
portion that is provided with a hard multilayer coating.
[0018] [FIG. 2] A cross sectional view showing a hard multilayer
coating as another example that is different from the hard
multilayer coating shown in view (c) of FIG. 1.
[0019] [FIG. 3] A view schematically showing, by way of example, an
arc-type ion plating apparatus that is capable of advantageously
forming the hard multilayer coatings of FIGS. 1 and 2.
[0020] [FIG. 4] A set of views showing result of measurement of
friction coefficients of CrN and TiAlN in comparison with each
other, wherein the measurement was made according to ball-on-disk
method.
[0021] [FIG. 5] A set of views for explaining result of measurement
of width of flank wear on each of coated cutting tools (including
invention products and comparative products) that are different
from each other with respect to composition of coating, wherein the
measurement was made after each coated cutting tool was used for
cutting C1100 (copper) at predetermined cutting conditions.
[0022] [FIG. 6] A set of views for explaining result of measurement
of width of flank wear on each of coated cutting tools (including
invention products and comparative products) that are different
from each other with respect to composition of coating, wherein the
measurement was made after each coated cutting tool was used for
cutting S50C (carbon steel for machine structural use) at
predetermined cutting conditions.
DESCRIPTION OF REFERENCE SIGNS
[0023] 10: ball endmill (hard multilayer coated tool) [0024] 12:
tool substrate (body) [0025] 20, 28: hard multilayer coating [0026]
22: backing layer [0027] 22a: TiAlN layer [0028] 22b: mixture layer
[0029] 24: intermediate layer [0030] 26: CrN layer
BEST MODE FOR CARRYING OUT THE INVENTION
[0031] The present invention may be advantageously applied to a
hard multilayer coating to be provided to cover a substrate of a
rotary cutting tool (e.g., end mill, drill and tap) having cutting
edges. However, the present invention may be applied also to any
other machining tool such as a non-rotary cutting tool (e.g.,
replaceable insert that is fixed to a tool holder used for a lathe
operation) and a cold-forming tool which is designed to form a
workpiece into a desired shape by plastically deforming the
workpiece. In addition, it may be applied also to a hard multilayer
coating to be provided as a surface-protecting coating to cover a
body or member (e.g., electronic component) which is other than the
machining-tools. It is noted that the substrate of the machining
tool, which is to be coated with the hard multilayer coating, is
preferably made of a cemented carbide or a high-speed tool steel.
However, the tool substrate may be made of any other metallic
material.
[0032] As a method of forming the hard multilayer coating according
to the present invention, an arc ion plating method is
advantageously employed. However, it is possible to employ other
physical vapor deposition (PVD) method such as a sputtering method,
or alternatively, a chemical vapor deposition (CVD) method such as
a plasma CVD method and a thermal CVD method.
[0033] It is preferable that the entire thickness of the hard
multilayer coating of the present invention is not larger than 10
.mu.m, since the coating would be easily peeled from the body if
the entire thickness is larger than 10 .mu.m. Further, where the
body has cutting edges, the entire thickness being larger than 10
.mu.m would cause the cutting edges to be rounded, thereby
deteriorating the cutting performance. It is preferable that the
thickness of the backing layer is not smaller than 2 .mu.m, since
it is not possible to obtain satisfactory coating performance and
strength such as sufficient wear resistance, heat resistance and
tenacity if the thickness of the backing layer is smaller than 2
.mu.m. Further, it is appropriate that the thickness of the backing
layer is not lager than 8 .mu.m in order that the entire thickness
of the hard multiplayer coating is not larger than 10 .mu.m.
[0034] It is appropriate that the thickness of the TiAlN layer
included in the backing layer is from 160 nm to 2000 nm, and that
the thickness of the TiAlN+CrN mixture layer included in the
backing layer is from 10 nm to 1000 nm, so that the wear resistance
can be maintained owing to the TiAlN layer while the chipping and
peeling are effectively prevented owing to the TiAlN+CrN mixture
layer. Where the backing layer includes a plurality of TiAlN layers
and a plurality of TiAlN+CrN mixture layers, the TiAlN layers may
have respective thicknesses equal to each other while the TiAlN+CrN
mixture layers may have the respective thicknesses equal to each
other. However, the TiAlN layers and the TiAlN+CrN mixture layers
may take any one of various arrangements such as an arrangement in
which the thicknesses of the TiAlN layers or the TiAlN+CrN mixture
layers are different from each other such that the thickness of the
layer is continuously changed. It is preferable that a mixed
crystal ratio between Ti and Al in the TiAlN layer included in the
backing layer is in a range from about 2:8 (=Ti:Al) to about 6:4
(=Ti:Al). A mixed crystal ratio between Ti and Al in TiAlN of the
TiAlN+CrN mixture layer, which is included in the backing layer or
provides the intermediate layer, may be substantially the same as
the mixed crystal ratio in the TiAlN layer, but does not have to be
necessarily the same as the mixed crystal ratio in the TiAlN
layer.
[0035] It is preferable that a total number of the TiAlN and
TiAlN+CrN mixture layers superposed on each other and constituting
the backing layer is at least three such that each of the lowermost
and uppermost layers of the backing layer is provided by the TiAlN
layer. However, the uppermost layer of the backing layer may be
provided by the TiAlN+CrN, mixture layer, for example, where the
thickness of the TiAlN+CrN mixture layer is so small as several
tens of nm. In such a case, the TiAlN+CrN mixture layer providing
the uppermost layer may be used as the intermediate layer, although
the intermediate layer consisting of another TiAlN+CrN mixture
layer may be provided in addition to the TiAlN+CrN mixture layer
providing the uppermost layer. The third invention encompass not
only an arrangement in which the uppermost layer of the backing
layer on which the CrN layer is directly disposed is provided by
the TiAlN layer but also an arrangement in which the uppermost
layer of the backing layer on which the CrN layer is directly
disposed is provided by the TiAlN+CrN mixture layer.
[0036] It is appropriate that the thickness of the intermediate
layer is not smaller than 0.1 .mu.m, since sufficient adhesiveness
among the layers cannot be obtained if the thickness of the
intermediate layer is smaller than 0.1 .mu.m. It is appropriate
that the thickness of the CrN layer constituting an uppermost
portion of the hard multilayer coating is not smaller than 0.1
.mu.m, since sufficient lubricity cannot be obtained if the
thickness of the CrN layer is smaller than 0.1 .mu.m. It is
preferable that the thickness of the CrN layer is not smaller than
0.5 .mu.m. In order that the entire thickness of the hard
multiplayer coating is not larger than 10 .mu.m, it is appropriate
that each of the thickness of the intermediate layer and the
thickness of the CrN layer is not larger than 5 .mu.m where the
hard multiplayer coating has the intermediate layer, and that the
thickness of the CrN layer is not larger than 8 .mu.m where the
hard multiplayer coating does not have the intermediate layer. In
order that the hard multiplayer coating has desired coating
strength and performance, it is appropriate that the entire
thickness of the hard multiplayer coating is not smaller than 2.1
.mu.m while the thickness of the backing layer is not smaller than
2 .mu.m where the hard multiplayer coating does not have the
intermediate layer, and that the entire thickness of the hard
multiplayer coating is not smaller than 2.2 .mu.m where the hard
multiplayer coating has the intermediate layer. It is preferable
that the entire thickness of the hard multiplayer coating is not
smaller than 2.5 .mu.m where the hard multiplayer coating has the
intermediate layer.
[0037] Each of the mixture layer of the backing layer and the
intermediate layer is provided by the TiAlN+CrN mixture layer.
Although the mixture layer of the backing layer and the
intermediate layer can be constituted by exactly the same
composition, they may be positively made different from each other
with respect to their compositions and characteristics, for
example, by changing layer forming conditions such as the mixed
crystal ratio between Ti and Al, mixing ratio between TiAlN and
CrN, and arc current and bias voltage applied upon layer
formation.
[0038] In the present invention, the CrN layer is provide to
constitute the uppermost portion of the hard multilayer coating.
However, in the first invention in which the intermediate layer
containing CrN is provided, it is possible to expect effect for
some improvement in the lubricity even if the intermediate layer is
arranged to constitute the uppermost portion of the hard multilayer
coating without provision of the CrN layer.
[0039] Each of the TiAlN layer, the TiAlN+CrN mixture layer
(including the intermediate layer) and the CrN layer may contain
carbon or other element in addition to inevitable impurity element,
as long as the contained other element does not impede a desired
effect favorable to the wear resistance, tenacity, adhesiveness,
heat resistance and welding resistance which are characteristics
required to the hard multilayer coating, namely, as long as the
contained other element does not considerably deteriorate these
characteristics. For example, not only pure nitride of chromium but
also CrCN that is carbonitride containing C (carbon) may be used as
CrN. Further, not only pure nitride of TiAl but also TiAlCN that is
carbonitride containing C (carbon) may be used as TiAlN.
EMBODIMENTS
[0040] There will be described in detail embodiments of the present
invention, with reference to the drawings.
[0041] FIG. 1 is a set of views showing a ball endmill 10 that is
one example of a hard-multilayer-coated rotary cutting tool to
which the present invention is applied, wherein view (a) is a front
view as seen in a direction perpendicular to an axis of the ball
endmill 10, and view (b) is an enlarged bottom view as seen from
side of a distal end of the ball endmill 10 (as seen from a right
side of the ball endmill 10 in view (a)). The ball endmill 10
includes a tool substrate 12 made of cemented carbide. The tool
substrate 12 has a cutting teeth portion 14 and a shank portion
that are formed integrally with each other. The cutting teeth
portion 14 is provided with cutting edges in the form of a pair of
peripheral cutting edges 16 and a pair of ball-nosed end cutting
edges 18, which are arranged to be symmetrical with each other with
respect to the axis, so that a cutting operation can be carried out
by the peripheral cutting edges 16 and the ball-nosed end cutting
edges 18 while the ball endmill 10 is being rotated about the axis.
The cutting teeth portion 14 is coated at its surface with a hard
multilayer coating 20 that is represented by an oblique-lined
portion in views (a), (b) of FIG. 1. View (c) of FIG. 1 is a cross
sectional view of a layered portion of the cutting teeth portion 14
that is coated with the hard multilayer coating 20. The ball
endmill 10 corresponds to a hard multilayer coated tool, while the
tool substrate 12 corresponds to a predetermined body on which the
hard multilayer coating 20 is disposed.
[0042] As is apparent from view (c) of FIG. 1, the hard multilayer
coating 20 is constituted by a backing layer 22, an intermediate
layer 24 and a CrN layer 26 that constitutes an outer surface and
an uppermost portion of the hard multilayer coating 20. The hard
multilayer coating 20 has an entire thickness of from 2.2 .mu.m to
10 .mu.m. The backing layer 22 consists of at least three layers
which include TiAlN layers 22a and TiAlN+CrN mixture layers 22b and
which are alternately superposed on each other. The backing layer
22 has a thickness of from 2 .mu.m to 8 .mu.m. Each of the TiAlN
layers 22a has an average thickness of from 160 nm to 2000 nm,
while each of the mixture layers 22b has an average thickness of
from 10 nm to 1000 nm. In the present embodiment, the TiAlN layers
22a having the same thickness and the mixture layers 22b having the
same thickness are alternately superposed on each other. Each of
the mixture layers 22b is a layer in which TiAlN and CrN are mixed
with a predetermined proportion therebetween. A mixed crystal ratio
between Ti and Al in TiAlN of the TiAlN layers 22a and the mixture
layers 22b is in a range from 2:8 (=Ti:Al) to 6:4 (=Ti:Al). In the
present embodiment, the mixed crystal ratio between Ti and Al is
4:6 (=Ti:Al). Each of the uppermost and lowermost layers of the
backing layer 22 is provided by the TiAlN layer 22a. The total
number of the TiAlN and mixture layers 22a, 22b is an odd number
that is not smaller than three.
[0043] TiAlN has a hardness (Hv) of about from 2300 to 3000, while
CrN has a hardness (Hv) of about from 1800 to 2300. Each mixture
layer 22b containing TiAlN and CrN has a hardness that is lower
than a hardness of each TiAlN layer 22a containing only TiAlN.
Therefore, in the backing layer 22 in which the TiAlN layers 22a
having the high hardness and the mixture layers 22b having the
relatively low hardness are alternately superposed on each other,
an excellent wear resistance is obtained owing to presence of the
TiAlN layers 22a having the high hardness, while an increased
tenacity is obtained owing to presence of the mixture layer 22b
having the low hardness, thereby reducing risk of chipping and
peeling of the coating 20. As described above, the average
thickness of each TiAlN layer 22a is from 160 nm to 2000 nm, the
average thickness of each mixture layer 22b is from 10 nm to 1000
nm, and the entire thickness of the backing layer 22 is from 2
.mu.m to 8 .mu.m, so that the wear resistance can be maintained
owing to the TiAlN layers 22a while the chipping and peeling can be
effectively prevented owing to the mixture layers 22b.
[0044] The intermediate layer 24 is a mixture layer in which TiAlN
and CrN are mixed to each other. In the present embodiment, the
intermediate layer 24 is the same as the mixture layers 22b with
respect to composition. The intermediate layer 24 is disposed on
the backing layer 22, described more specifically, is disposed to
be contiguous to the TiAlN layer 22a as the uppermost layer of the
backing layer 22. The thickness of the intermediate layer 24 is
from 0.1 .mu.m to 5 .mu.m. Thus, the intermediate layer 24 of
TiAlN+CrN is disposed on the backing layer 24, i.e., on the
uppermost TiAlN layer 22a, before disposition of the CrN layer 26,
whereby the adhesiveness of the CrN layer 26 with respect to the
backing layer 22 is improved. A mixed crystal ratio between Ti and
Al in TiAlN of the intermediate layer 24 is in a range from 2:8
(=Ti:Al) to 6:4 (=Ti:Al). In the present embodiment, the mixed
crystal ratio between Ti and Al is 4:6 (=Ti:Al).
[0045] The CrN layer 26 is disposed on and contiguous to the
intermediate layer 24, and has a thickness of from 0.1 .mu.m to 5
.mu.m. CrN constituting the CrN layer 26 has a coefficient of
friction lower than that of TiAlN. Therefore, owing to the CrN
layer 26 provided to constitute the outer surface and the uppermost
portion of the hard multilayer coating 20, it is possible to
improve lubricity between the coating 20 and a workpiece, namely,
improve resistance to welding between the coating 20 and the
workpiece.
[0046] FIG. 4 is a set of views showing result of measurement of
friction coefficients of CrN and TiAlN that was made according to
ball-on-disk method, which is substantially the same as a test
method defined in JIS R1613. In FIG. 4, view (a) shows conditions
of the test, and view (b) shows a result of the test. Friction
coefficient curves of the view (b) represents a change of each of
the friction coefficients in an initial period. The friction
coefficient of TiAlN is converged within a range about from 0.5 to
0.7, while the friction coefficient of CrN is converged to about
0.3. Further, view (c) of FIG. 4 shows the friction coefficients
measured at a high temperature (400.degree. C.). The friction
coefficient of TiAlN measured at the high temperature is about 0.7,
while the friction coefficient of CrN measured at the high
temperature is about 0.25. Thus, the friction coefficients measured
at the high temperature are substantially the same as those
measured at a room temperature (25.degree. C.) and shown in view
(b) of FIG. 4. It is noted that the friction coefficients shown in
view (c) of FIG. 4 were measured at the same test conditions as
those shown in view (a) of FIG. 4 except that the temperature was
400.degree. C.
[0047] Although the above-described hard multilayer coating 20
includes the intermediate layer 24, the CrN layer 26 may be
disposed directly on the backing layer 22 with the intermediate
layer 24 being omitted, as in a hard multilayer coating 28 of FIG.
2. In this case, the backing layer 22 may have substantially the
same construction as in the hard multilayer coating 20, and the
thickness of the CrN layer 26 can be increased owing to absence of
the intermediate layer 24. Thus, the thickness of the CrN layer 26
may be from 0.1 .mu.m to 8 .mu.m.
[0048] TiAlN contained in the TiAlN layers 22a and the mixture
layers 22b of the backing layer 22 and the intermediate layer 24 is
pure nitride of TiAl that does not include carbon. However, the
pure nitride of TiAl is replaced by TiAlCN that is carbonitride
containing carbon whose amount is determined such that the
hardness, adhesiveness and other characteristic are not
deteriorated. CrN contained in the mixture layers 22b of the
backing layer 22, the intermediate layer 24 and the CrN layer 26 is
pure nitride of chromium that does not include carbon. However, the
pure nitride of chromium is replaced by CrCN that is carbonitride
containing carbon whose amount is determined such that the
lubricity, heat resistance and other characteristic are not
deteriorated.
[0049] On the other hand, FIG. 3 is a schematic view (schematic
diagram) showing an arc-type ion plating apparatus 30 which can be
advantageously used for forming the hard multilayer coating 20 or
28. The arc-type ion plating apparatus 30 includes: a holding
member 32 for holding a multiplicity of intermediate products in
the form of the substrates 12 each of which is not yet coated with
the hard multilayer coating 20 or 28 and has the cutting edges 16,
18 already formed therein; a rotary device 34 for rotating the
holding member 32 about a rotation axis which extends substantially
in a vertical direction; a bias-voltage power source 36 for
applying a negative bias voltage to the substrates 12; a processing
vessel in the form of a chamber 38 which accommodates therein the
substrates 12; first and second arc-discharge power sources 44, 46;
a reaction-gas supplying device 40 for supplying a reaction gas
into the chamber 38; and a vacuum device 42 for sucking a gas in
the interior of the reactor 22 with, for example, a vacuum pump so
as to reduce the pressure in the interior of the chamber 38. The
holding member 32 consists of a cylindrical or prism member having
a center at the above-described rotation axis. The multiplicity of
substrates 12 are held by the holding member 32 such that each
substrate 12 takes a substantially horizontal posture with the
cutting teeth portion 14 protruding outwardly in a radial direction
of the holding member 32. The reaction-gas supplying device 40 is
equipped with a tank in which nitrogen gas (N.sub.2) is stored, so
that nitride of TiAl and nitride of Cr can be formed by supplying
the nitrogen gas into the chamber 38. It is noted that, where
carbonitride of TiAl and carbonitride of Cr are to be formed, a
tank storing therein hydrocarbon gas (CH.sub.4, C.sub.2H.sub.2,
etc.) is provided so that the hydrocarbon gas as well as the
nitrogen gas is supplied.
[0050] The first arc-discharge power source 44 is connected to a
first evaporation source (target) 48 as a cathode that is formed of
TiAl alloy constituting TiAlN contained in the TiAlN layers 22a and
the mixture layers 22b, and is connected also to an anode 50. The
first arc-discharge power source 44 serves to supply a
predetermined amount of an arc current between the first
evaporation source 48 and the anode 50, for causing arc discharge
therebetween, so that TiAl is evaporated from the first evaporation
source 48. The evaporated TiAl becomes metallic ions (positive
ions), and then adheres to the tool substrates 12 to which the
negative bias voltage is applied by the bias-voltage power source
36. Similarly, the second arc-discharge power source 46 is
connected to a second evaporation source (target) 52 as a cathode
that is formed of Cr constituting CrN contained in the mixture
layers 22b, the intermediate layer 24 and the CrN layer 26, and is
connected also to an anode 54. The second arc-discharge power
source 46 serves to supply a predetermined amount of an arc current
between the second evaporation source 52 and the anode 54, for
causing arc discharge therebetween, so that Cr is evaporated from
the second evaporation source 52. The evaporated Cr becomes
metallic ions (positive ions), and then adheres to the tool
substrates 12 to which the negative bias voltage is applied by the
bias-voltage power source 36.
[0051] When the hard multilayer coating 20 or 28 is to be formed on
a surface of the cutting teeth portion 14 of the tool substrate 12,
by using the arc-type ion plating apparatus 30, the pressure in the
interior of the chamber 38 is held in a predetermined value (which
ranges, for example, from 1.33.times.5.times.10.sup.-1 Pa to
1.33.times.40.times.10.sup.-1 Pa) by the reaction-gas supplying
device 40 and the vacuum device 42, while a predetermined value of
the negative bias voltage (which ranges, for example, from -50V to
-150V) is applied to the tool substrate 12 by the bias-voltage
power source 36. In this instance, the vacuum device 42 vacuums the
chamber 30, and at the same time the reaction-gas supplying device
40 supplies the reaction gas into the chamber 30 in such a manner
that holds the pressure in the interior of the chamber 30 in the
above-described predetermined value. Then, while the rotary device
34 is activated to rotate the holding member 32 at a predetermined
number of revolutions (for example, 3 min.sup.-1), the hard
multilayer coating 20 or 28 is formed on the tool substrate 12, by
selectively energizing (ON) and deenergizing (OFF) the first and
second arc-discharge power sources 44, 46.
[0052] Described specifically, when the first arc-discharge power
source 44 is kept ON (energized) while the second arc-discharge
power source 46 is kept OFF (deenergized), the arc current is
supplied between the first evaporation source 48 and the anode 50
so as to cause a metal ion of TiAl to be emitted from the first
evaporation source 48. The emitted metal ion of TiAl reacts with
the nitrogen gas, so that TiAlN is formed and adheres to the
surface of the tool substrate 12, whereby the TiAlN layer 22a can
be formed. The value of the arc current supplied by the first
arc-discharge power source 44 and the power-on time for which the
first arc-discharge power source 44 is kept ON are determined based
on the desired thickness of the TiAlN layer 22a.
[0053] Further, when the second arc-discharge power source 46 is
kept ON (energized) while the first arc-discharge power source 44
is kept OFF (deenergized), the arc current is supplied between the
second evaporation source 52 and the anode 54 so as to cause a
metal ion of Cr to be emitted from the first evaporation source 48.
The emitted metal ion of Cr reacts with the nitrogen gas, so that
CrN is formed and adheres to the surface of the tool substrate 12,
whereby the CrN layer 26 can be formed. The value of the arc
current supplied by the second arc-discharge power source 46 and
the power-on time for which the second arc-discharge power source
46 is kept ON are determined based on the desired thickness of the
CrN layer 26.
[0054] Further, when the first and second arc-discharge power
sources 44, 46 are both kept ON (energized), the arc current is
supplied between the first evaporation source 48 and the anode 50
while the arc current is supplied between the second evaporation
source 52 and the anode 54. In this case, the metal ion of TiAl is
emitted from the first evaporation source 48 while the metal ion of
Cr is emitted from the second evaporation source 52. The emitted
metal ion of TiAl and metal ion of Cr react with the nitrogen gas,
so that the TiAlN and CrN are formed and adhere to the surface of
the tool substrate 12. Since the first evaporation source 48 and
the second evaporation source 52 are disposed on respective
opposite sides of the holding member 32, TiAlN and CrN alternately
adhere to the surface of the tool substrate 12 as the holding
member 32 is rotated, so that it is possible to form the mixture
layer 22b and the intermediate layer 24 in which TiAlN and CrN are
mixed to each other. The power-on times for which the first and
second arc-discharge power sources 44, 46 are kept ON are
determined based on the desired thicknesses of the mixture layer
22b and the intermediate layer 24. The values of the arc currents
supplied by the first and second arc-discharge power sources 44, 46
are determined based on the desired thicknesses of the mixture
layer 22b and the intermediate layer 24 and mixing ratio between
TiAlN and CrN.
[0055] Thus, by switching each of the first and second
arc-discharge power sources 44, 46 between its energized and
deenergized states (ON and OFF states), it is possible to
continuously form the backing layer 22 (including the TiAlN layers
22a and the TiAlN+CrN mixture layers 22b that are alternately
superposed on each other), the intermediate layer 24 consisting of
the TiAlN+CrN mixture layer, and the CrN layer 26, so that the hard
multilayer coating 20, 28 can be disposed on the surface of the
tool substrate 12. The operation for formation of the hard
multilayer coating 20, 28 such as switching of each of the first
and second arc-discharge power sources 44, 46 can be automatically
carried out by a control device including a computer.
[0056] In the hard multilayer coating 20, 28 of the present
embodiments, owing to presence of the backing layer 22 including
the TiAlN layers 22a and the TiAlN+CrN mixture layers 22b that are
alternately superposed on each other, it is possible to obtain
excellent wear resistance and tenacity. Further, since the CrN
layer 26 constitutes an uppermost portion of the hard multilayer
coating 20, 28 and providing the surface of the hard multilayer
coating 20, 28 has a low coefficient of friction, it is possible to
improve lubricity and welding resistance. Further, since an
oxidation initiation temperature of the CrN layer 26 is as high as
about 700.degree. C., excellent characteristics of the coating are
stably maintained even in an environment of high temperature.
[0057] Therefore, in the ball endmill 10 coated with the hard
multilayer coating 20, 28, it is possible to obtain excellent
cutting performance and durability in a wide range of use, for
example, from a case of cutting a workpiece made of ferrous or
non-ferrous (e.g., copper alloy) material having a low hardness and
easily weldable, to a case of cutting a workpiece made of a high
hardness material such as heat treated steel having a hardness of
about 50 HRC. Specifically described, owing to presence of the CrN
layer 26, it is possible to restrain wear on each rake face and to
restrain change of the rake angle toward the negative side in a
late stage of the cutting operation, so that a cutting capacity is
satisfactorily maintained for a long term, thereby improving the
durability of the tool and stabilizing the quality of the finished
surface of the workpiece. The ball endmill 10 has a distal end
portion which is located around its axis of rotation, and the
workpiece is easily weldable to the distal end portion due to a low
cutting capacity of the distal end portion. However, owing to the
presence of the CrN layer 26, the welding can be restrained whereby
the cutting performance and the durability can be satisfactorily
maintained. Further, since the excellent characteristics of the
coating can be stably obtained even in the environment of high
temperature, the cutting tool is capable of carrying out a cutting
operation with high efficiency under a tough cutting condition with
a high temperature caused by, for example, frictional heat.
[0058] In the present embodiments in which each of the lowermost
layer and the uppermost layer of the backing layer 22 is provided
by the TiAlN layer 22a, the backing layer 22 can be adhered to the
tool substrate 12 with excellent adhesiveness owing to the TiAlN
layer 22a providing the lowermost layer, while the backing layer 22
can have excellent wear resistance owing to the TiAlN layer 22a
providing the uppermost layer. Since the CrN layer 26 is disposed
on the TiAlN layer 22a providing the uppermost layer directly or
through the intermediate layer 24, the TiAlN layer 22a having the
high hardness is not brought into direct contact with the
workpiece. However, the TiAlN layer 22a serves to restrain
deformation of the CrN layer 26, so that wear resistance of the CrN
layer 26 is improved.
[0059] Further, in the hard multilayer coating 20 of FIG. 1, since
the intermediate layer 24 consisting of the TiAlN+CrN mixture layer
(containing CrN) is interposed between the backing layer 22 and the
CrN layer 26, the CrN layer 26 is superposed with high adhesiveness
with respect to the backing layer 22 whose uppermost layer is
provided by the TiAlN layer 22a, so that chipping and peeling of
the CrN layer 26 can be further advantageously restrained.
[0060] Further, in the hard multilayer coating 20, 28 of the
present embodiments, since the entire thickness of the coating 20,
28 is not larger than 10 .mu.m, it is possible to restrain the
peeling of the coating 20, 28 from the tool substrate 12, so as to
obtain excellent adhesiveness between the coating 20, 28 and the
tool substrate 12. In addition, owing to the entire thickness being
not larger than 10 .mu.m, it is also possible to avoid the
peripheral and ball-nosed end cutting edges 16, 18 from being
rounded, so that deterioration of the cutting performance is
prevented. Meanwhile, since the entire thickness of the coating 20,
28 is not smaller than 2.2 .mu.m, it is possible to obtain
predetermined coating strength and performance. That is, since the
thickness of the backing layer 22 is not smaller than 2 .mu.m, it
is possible to obtain coating performance and strength required to
the backing layer 22 such as sufficient wear resistance, heat
resistance and tenacity. Moreover, since the thickness of each of
the intermediate layer 24 and the CrN layer 26 is not smaller than
0.1 .mu.m, it is possible to obtain coating performance such as
sufficient adhesiveness and lubricity.
[0061] FIG. 5 is a set of views showing result of measurement of VB
wear width (width of flank wear) on each of the ball endmills 10
having the respective ball-nosed end cutting edges 18 whose radius
R is 1.5 mm, wherein the measurement was made after each ball
endmill 10 was used for cutting C1100 (JIS: copper) for a distance
of 400 mm under cutting conditions indicated in view (a) of FIG. 5.
The ball endmills 10 had respective various coatings indicated in
view (b) of FIG. 5. As shown in view (b) of FIG. 5, the VB wear
widths on the present invention products ranged from 0.035 .mu.m to
0.049 .mu.m, so that it can be understood that the invention
products have wear resistance improved over the comparative
products and also excellent durability even against an easily
weldable workpiece such as copper. For example, the durability of
each of the invention products is at least twice as high as the
durability of the comparative product (conventional product) with
the coating consisting of only the backing layer 22 having a
multilayered construction, since the VB wear width on that
comparative product was 0.093 .mu.m. It is noted that, in the
comparative products as well as in the invention products, each of
the uppermost and lowermost layers of the backing layer 22 having
the multilayered construction (in which the TiAlN layers 22a and
the TiAlN+CrN mixture layers 22b are alternately superposed on each
other) is provided by the TiAlN layer 22a.
[0062] FIG. 6 is a set of views showing result of measurement of VB
wear width (width of flank wear) on each of the ball endmills 10
having the respective ball-nosed end cutting edges 18 whose radius
R is 3 mm, wherein the measurement was made after each ball endmill
10 was used for cutting S50C (JIS: carbon steel for machine
structural use) for a distance of 56 mm under cutting conditions
indicated in view (a) of FIG. 6. The ball endmills 10 had
respective various coatings indicated in view (b) of FIG. 6. As
shown in view (b) of FIG. 6, the VB wear widths on the present
invention products ranged from 0.063 .mu.m to 0.078 .mu.m, so that
it can be understood that the invention products have wear
resistance improved over the comparative products and also
excellent durability even against a workpiece made of a high
hardness material such as carbon steel. For example, the durability
of each of the invention products is improved by 10% over the
comparative product (conventional product) with the coating
consisting of only the backing layer 22 having a multilayered
construction, since the VB wear width on that comparative product
was 0.091 .mu.m. It is noted that, in the comparative products as
well as in the invention products, each of the uppermost and
lowermost layers of the backing layer 22 having the multilayered
construction (in which the TiAlN layers 22a and the TiAlN+CrN
mixture layers 22b are alternately superposed on each other) is
provided by the TiAlN layer 22a.
[0063] While the presently preferred embodiments of the present
invention have been illustrated above, it is to be understood that
the invention is not limited to the details of the illustrated
embodiments, but may be embodied with various other changes,
modifications and improvements, which may occur to those skilled in
the art, without departing from the spirit and scope of the
invention defined in the following claims.
INDUSTRIAL APPLICABILITY
[0064] Since the hard multilayer coating of the present invention
has sufficient wear resistance and welding resistance, where the
hard multilayer coating is disposed on a surface of a tool
substrate of a rotary cutting tool or the like, it is possible to
obtain excellent cutting performance and durability in a wide range
of use, for example, from a case of cutting a workpiece made of
copper alloy or other material having a low hardness and easily
weldable, to a case of cutting a workpiece made of heat treated
steel or other material having a high hardness. Therefore, the hard
multilayer coating of the present invention is advantageously used
as a hard coating that is to be disposed on a surface of a cutting
tool such as a ball endmill. In addition, it may be applied also to
a coating that is to be provided, for example, as a
surface-protecting coating of a body such as an electronic
component, which is other than the machining tools.
* * * * *